The 119 acts the same as the 117, as they start in the same place, Piazza del Popolo.
On Saturdays, or the days before a holiday (called prefestivi), the 117 bus does not operate from Piazza di Popolo because of the closure of traffic on Via del Corso between 15:00 and 20:00
These two posts on the 117 might describe this in more detail:
Bus 117 to Piazza San Giovanni in Laterano and
Bus 117 to Piazza del Popolo